(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of preventing silicon pits in the active region in the fabrication of integrated circuits.
(2) Description of the Prior Art
As device sizes shrink into the sub-micron and sub-half-micron regime, it has become necessary to use a combination of polysilicon and refractory metal silicides as the material for gate electrodes and interconnection lines because of their reduced resistivity. It is also essential to keep the active regions as free from defects as possible. Pitting of the silicon in the active areas can cause junction leakage and low yields. FIG. 1 illustrates a partially completed integrated circuit device in which voids 20 form at the interface between a polysilicon layer 16 and a silicide layer 18 after deposition of a tetraethoxysilane (TEOS) layer 19. When the polysilicon and silicide layers are patterned to form a gate electrode, as illustrated in FIG. 2, pits 22 are formed in the silicon where the voids were located.
The paper, "Oxidation Phenomena of Polysilicon/Tungsten Silicide Structures," by N. Hsieh, Journal of the Electrochemical Society, January 1984, pp. 201-205, discusses the formation of voids in a polysilicon layer under a silicide layer. The voids form as a result of pinholes in the native oxide layer between the polysilicon and the silicide layers. In the paper, "Controlling Void Formation in WSi.sub.2 Polycides," by C. W. Koburger et al, IEEE Electron Device Letters, Vol. EDL-5, No. 5, May 1984, pp. 166-168, the authors also discuss void formation in the polysilicon layer under a silicide layer. They prevent the formation of these voids by depositing a capping layer of polysilicon over the silicide prior to oxidation.
Workers in the art have used ion implantation in the manufacture of integrated circuit devices. U.S. Pat. No. 5,541,131 to Yoo et al implants silicon ions into the top surface of the silicide layer of a polycide gate electrode as a silicon source during oxidation or annealing to prevent stress and thus to prevent peeling of the silicide layer. U.S. Pat. No. 5,624,869 to Agnello et al implants platinum or nitrogen ions into a cobalt silicide layer to preserve the structure under thermal stress. U.S. Pat. No. 5,444,024 to Anjum et al implants argon ions into a silicide layer to prevent underlying silicon from diffusing into the silicide. U.S. Pat. No. 5,654,241 to Kakumu implants metal ions into silicon and then heat-treats the silicon to form a silicide. None of these workers describe a solution to the silicon pitting problem described above.